| Regulation of the ER 81 transcription factor and its coactivators by mitogen and stress activated protein kinase 1 ( MSK 1 ) . ^^^ Here , mitogen and stress activated protein kinase 1 ( MSK 1 ) , which itself is directly activated by distinct classes of MAPKs , is identified to regulate ER 81 function . ^^^ MSK 1 expression enhances ER 81 dependent transcription upon stimulation of especially the p 38 MAPK pathway . ^^^ Two serine residues in ER 81 are phosphorylated by MSK 1 , and mutating these serine residues to alanines dramatically diminishes the ability of MSK 1 to stimulate ER 81 . ^^^ However , mutation of the MSK 1 phosphorylation sites in ER 81 does not completely abrogate the ability of MSK 1 to activate ER 81 function , suggesting that MSK 1 may also target cofactors of ER 81 . ^^^ |